The effects of climate change on birdlife may be more complex than predicted, the findings of an exhaustive survey of Finnish species suggests.
Several studies have shown that global warming represents a major threat to biodiversity.
In a European context, modelling suggests that in coming years there will be a broad drift of bird species northwards as those historically resident in southern latitudes shift range in response to rising temperatures.
In the higher latitudes, therefore, the overall number of species – “species richness”, in the jargon – is predicted to increase.
A study comparing bird numbers and species distribution in Finland across a 35-year period has found evidence to support the first of those contentions, but not the second.
Raimo Virkkala from the Natural Environment Centre and Aleksi Lehikoinen from the Finnish Museum of Natural History, both in Helsinki, used two sets of bird mapping data for all 235 species native to the country, covering a swathe of land 1,100 kilometres wide, comprising 300,000 square kilometres.
The first dataset was compiled between 1974 and 1989; the second between 2006 and 2010. Both used identical 10 kilometre-square grids.
Comparing the sets, the researchers found that all but one of the species mapped had altered ranges. Some 37% had increased their presence, and 35% had shrunk.
Non-migratory birds were more likely to have expanded their ranges, while migratory species in general occupied less territory. The reduction in migratory bird range, write Virkkala and Lehikoinen, is “in line with the observed population declines of long-distance migrants in the whole [of] Europe”.
While ranges expanded or declined, depending on the bird, overall species richness remained unchanged.
Modelling the effects of global warming on bird species numbers and distribution is complicated by the changing dynamics of human activity prompted by the same stimulus.
“The results show that there is an ongoing considerable species turnover due to climate change and due to land use and other direct human influence,” the scientists observe.
They go on to warn that the type of changes to avian populations in the Finland may be harbingers of long term, perhaps permanent, alterations to ecosystems.
“High bird species turnover observed in northern Europe may also affect the functional diversity of species communities,” they conclude.